Abstract: The water level-discharge relationship is crucial for obtaining hydrological information and studying the hydrodynamic environment of river systems.In tidal river reaches, hydrological stations typically observe only tidal level data, requiring real-time discharge to be estimated through the water level-discharge relationship.Using Shizui Station on the Tanjiang River as a case study, this study applies tidal harmonic analysis to investigate tidal variation patterns and the contributions of constituent tides.Tidal level data (excluding runoff influence) and river water levels (excluding tidal effects) are extracted.Based on the HEC-RAS one-dimensional hydrodynamic model, flow variations under different water level scenarios are simulated, and multiple regression analysis is conducted to examine the water level-discharge relationship.The results indicate that the water level-discharge relationship at Shizui Station is jointly influenced by tidal flow and river runoff.Tidal flow dominates real-time discharge variations, exhibiting an unstable, non-unique hysteresis loop pattern, whereas river runoff demonstrates a stable but non-unique relationship.These findings can aid in analyzing water level-discharge relationships in tidal river reaches lacking measured discharge data, supporting hydrological forecasting and hydrodynamic environment studies.